Electronic dimming ballast

Abstract

An electronic dimming ballast has a parallel loaded resonant output circuit plus a combination of pulse width modulation and frequency variation to accomplish the dimming of compact fluorescent lamps. The ballast operates at a fixed frequency throughout a selected range of light levels, with dimming control being done completely by duty cycle variation over this range of operation, and then smoothly moves to a variable frequency as the light output moves outside the selected range, with both duty cycle and frequency variation being the means of lamp light output control outside the selected range.

What is claimed is:  
     
       1. An electronic dimming ballast for fluorescent lamps, comprising 
       a circuit comprising at least one controllably conductive device for supplying a selected arc current to a fluorescent lamp to achieve a desired light output level from the lamp,  
       a first circuit responsive to a dimming signal containing information representative of the desired light output level and generating an ac oscillator signal having a frequency determined by the dimming signal, and  
       a second circuit responsive to the dimming signal for creating a duty cycle of operation for the at least one controllably conductive device at the frequency of the ac oscillator signal, the duty cycle being determined by the dimming signal, whereby the frequency and the duty cycle of operation of the at least one controllably conductive device arc independently determinable over a range of desired light output levels of the lamp.  
     
     
       2. An electronic dimming ballast according to  claim 1 , wherein the first circuit and the second circuit have at least one circuit element in common. 
     
     
       3. An electronic dimming ballast for fluorescent lamps, comprising 
       an inverter circuit comprising at least one controllably conductive device for supplying a selected arc current to a fluorescent lamp to achieve a desired light output level from the lamp ranging from a minimum light output to a maximum light output,  
       a first circuit for receiving a dimming signal containing information representative of a desired light level and generating a control signal representative of the desired light level,  
       a second circuit responsive to the control signal for generating an ac oscillator signal having a frequency determined by the control signal, and  
       a third circuit responsive to the control signal for creating a duty cycle of operation for the at least one controllably conductive device at the frequency of the ac oscillator signal, the duty cycle being determined by the control signal, whereby the frequency and the duty cycle of operation of the at least one controllably conductive device arc independently determinable over the range of desired light levels from the minimum light output up to the maximum light output.  
     
     
       4. An electronic dimming ballast for fluorescent lamps according to  claim 3 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of desired light levels from the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is variable over a range of desired light levels from the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is substantially constant over a range of desired light levels from the intermediate light output up to the maximum light output. 
     
     
       5. An electronic dimming ballast for fluorescent lamps according to  claim 3 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of desired light levels from the minimun light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant over a range of desired light levels from the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is variable over a range of desired light levels above the intermediate light output. 
     
     
       6. An electronic dimming ballast for fluorescent lamps according to  claim 3 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of desired light levels from the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant over a range of desired light levels from the minimum light output up to a first light output intermediate the minimum light output and the maximum light output, is variable over a range of desired light levels from the first light output up to a second light output intermediate the first light output and the maximum light output, and is substantially constant over a range of desired light levels from the second light output up to the maximum light output. 
     
     
       7. An electronic dimming ballast according to  claim 3 , wherein the second circuit and the third circuit have at least one circuit element in common. 
     
     
       8. An electronic dimming ballast for fluorescent lamps, comprising 
       an inverter circuit comprising at least one controllably conductive device for supplying a selected arc current to a fluorescent lamp to achieve a desired light output level from the lamp ranging from a minimum light output to a maximum light output,  
       a first circuit for receiving a dimming signal having a variable duty cycle and generating a control signal representative of the duty cycle of the dimming signal,  
       a second circuit responsive to the control signal for generating an ac oscillator signal having a frequency determined by the control signal, and  
       a third circuit responsive to the control signal for creating a duty cycle of operation for the at least one controllably conductive device at the frequency of the ac oscillator signal, the duty cycle being determined by the control signal, whereby the frequency and the duty cycle of operation of the at least one controllably conductive device arc independently determinable over the range of desired light levels from the minimum light output up to the maximum light output.  
     
     
       9. An electronic dimming ballast for fluorescent lamps according to  claim 8 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of dimming signal duty cycles corresponding to the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is variable over a range of dimming signal duty cycles corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is substantially constant over a range of dimming signal duty cycles corresponding to the intermediate light output up to the maximum light output. 
     
     
       10. An electronic dimming ballast for fluorescent lamps according to  claim 8 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of dimming signal duty cycles corresponding to the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant over a range of dimming signal duty cycles corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is variable over a range of dimming signal duty cycles above that corresponding to the intermediate light output. 
     
     
       11. An electronic dimming ballast for fluorescent lamps according to  claim 8 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of dimming signal duty cycles corresponding to the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant over a range of dimming signal duty cycles corresponding to the minimum light output up to a first light output intermediate the minimum light output and the maximum light output, is variable over a range of dimming signal duty cycles corresponding to the first light output up to a second light output intermediate the first light output and the maximum light output, and is substantially constant over a range of dimming signal duty cycles corresponding to the second light output up to the maximum light output. 
     
     
       12. An electronic dimming ballast according to  claim 8 , wherein the second circuit and the third circuit have at least one circuit element in common. 
     
     
       13. A dimming circuit for selectably controlling the light output of a fluorescent lamp, comprising 
       a dimming control circuit for generating a dimming signal representing a specified light output of the lamp in a range from a minimum light output of the lamp to a maximum light output of the lamp,  
       an inverter circuit comprising at least one controllably conductive device for supplying a selected arc current to the fluorescent lamp to achieve a desired light output level from the fluorscent lamp ranging from a minimum light output to a maximum light output,  
       a first circuit for receiving said dimming signal and generating a control signal representative of the specified light output,  
       a second circuit responsive to the control signal for generating an ac oscillator signal having a frequency determined by the control signal, and  
       a third circuit responsive to the control signal for creating a duty cycle of operation for the at least one controllably conductive device at the frequency of the ac oscillator signal, the duty cycle being determined by the control signal, whereby the frequency and the duty cycle of operation of the at least one controllably conductive device are independently determinable for specified light outputs of the lamp from the minimum light output up to the maximum light output.  
     
     
       14. An electronic dimming ballast according to  claim 13 , wherein the second circuit and the third circuit have at least one circuit element in common. 
     
     
       15. A dimming circuit for selectably controlling the light output of a fluorescent lamp according to  claim 13 , wherein the duty cycle of operation of the at least one controllably conductive device is variable for specified light outputs from the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is variable for specified light outputs from the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is substantially constant for specified light outputs from the intermediate light output up to the maximum light output. 
     
     
       16. A dimming circuit for selectably controlling the light output of a fluorescent lamp according to  claim 13 , wherein the duty cycle of operation of the at least one controllably conductive device is variable for specified light outputs from the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant for specified light outputs from the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is variable for specified light outputs in a range above the intermediate light output. 
     
     
       17. A dimming circuit for selectably controlling the light output of a fluorescent lamp according to  claim 13 , wherein the duty cycle of operation of the at least one controllably conductive device is variable for specified light outputs from the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant for specified light outputs from the minimum light output up to a first light output intermediate the minimum light output and the maximum light output, is variable for specified light outputs from the first light output up to a second light output intermediate the first light output and the maximum light output, and is substantially constant for specified light outputs from the second light output up to the maximum light output. 
     
     
       18. A dimming circuit for selectably controlling the light output of a fluorescent lamp, comprising 
       a dimming control circuit for generating a variable duty cycle dimming signal, the duty cycle being variable over a range of duty cycles from a minimum duty cycle corresponding to a minimum light output of the lamp to a maximum duty cycle corresponding to a maximum light output of the lamp,  
       an inverter circuit comprising at least one controllably conductive device for supplying a selected arc current to the fluorescent lamp to achieve a desired light output from the fluorescent lamp ranging from a minimum light output to a maximum light output,  
       a first circuit for receiving said variable duty cycle dimming signal and generating a control signal representative of the duty cycle of the dimming signal,  
       a second circuit responsive to the control signal for generating an ac oscillator signal having a frequency determined by the control signal, and  
       a third circuit responsive to the control signal for creating a duty cycle of operation for the at least one controllably conductive device at the frequency of the ac oscillator signal, the duty cycle of operation being determined by the control signal, whereby the frequency and the duty cycle of operation of the at least one controllably conductive device are independently determinable over the range of lamp light outputs from the minimum light output up to the maximum light output.  
     
     
       19. A dimming circuit for selectably controlling the light output of a fluorescent lamp according to  claim 18 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of dimming signal duty cycles corresponding to the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is variable over a range of dimming signal duty cycles corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is substantially constant over a range of dimming signal duty cycles corresponding to the intermediate light output up to the maximum light output. 
     
     
       20. A dimming circuit for selectably controlling the light output of a fluorescent lamp according to  claim 18 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of dimming signal duty cycles corresponding to the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant over a range of dimming signal duty cycles corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and is variable over a range of dimming signal duty cycles corresponding to light output above the intermediate light output. 
     
     
       21. An electronic dimming ballast according to  claim 18 , wherein the second circuit and the third circuit have at least one circuit element in common. 
     
     
       22. A dimming circuit for selectably controlling the light output of a fluorescent lamp according to  claim 18 , wherein the duty cycle of operation of the at least one controllably conductive device is variable over the range of dimming signal duty cycles corresponding to the minimum light output up to the maximum light output and the frequency of operation of the at least one controllably conductive device is substantially constant over a range of dimming signal duty cycles corresponding to the minimum light output up to a first light output intermediate the minimum light output and the maximum light output, is variable over a range of dimming signal duty cycles corresponding to the first light output up to a second light output intermediate the first light output and the maximum light output, and is substantially constant over a range of dimming signal duty cycles corresponding to the second light output up to the maximum light output. 
     
     
       23. A method of selectably controlling the light output of a fluorescent lamp using an inverter circuit having at least one controllably conductive device for supplying a selected arc current to the fluorescent lamp to achieve a desired light output from the fluorescent lamp ranging from a minimum light output to a maximum light output, comprising the steps of 
       generating a dimming signal variable from a state corresponding to a minimum light output of the lamp to a state corresponding to a maximum light output of the lamp,  
       generating a control signal representative of the dimming signal,  
       generating an ac oscillator signal having a frequency determined by the control signal, and  
       generating a duty cycle of operation for the at least one controllably conductive device at the frequency of the ac oscillator signal, the duty cycle being determined by the control signal, whereby the frequency and the duty cycle of operation of the at least one controllably conductive device are independently determinable over the range of dimming signals variable from the state corresponding to the minimum light output up to the maximum light output.  
     
     
       24. A method of selectably controlling the light output of a fluorescent lamp according to  claim 23 , wherein the step of generating the ac oscillator signal comprises varying the ac oscillator signal frequency for states of the dimming signal corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and maintaining the frequency substantially constant for states of the dimming signal corresponding to the intermediate light output up to the maximum light output. 
     
     
       25. A method of selectably controlling the light output of a fluorescent lamp according to  claim 23 , wherein the step of generating the ac oscillator signal comprises maintaining the ac oscillator signal frequency substantially constant for states of the dimming signal corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and varying the frequency for states of the dimming signal corresponding to a range of light outputs above the intermediate light output. 
     
     
       26. A method of selectably controlling the light output of a fluorescent lamp according to  claim 23 , wherein the step of generating the ac oscillator signal comprises maintaining the ac oscillator signal frequency substantially constant for states of the dimming signal corresponding to the minimum light output up to a first light output intermediate the minimum light output and the maximum light output, varying the frequency for states of the dimming signal corresponding to the first light output up to a second light output intermediate the first light output and the maximum light output, and maintaining the frequency substantially constant for states of the dimming signal corresponding to the second light output up to the maximum light output. 
     
     
       27. A method of selectably controlling the light output of a fluorescent lamp using an inverter circuit having at least one controllably conductive device for supplying a selected arc current to the fluorescent lamp to achieve a desired light output from the lamp ranging from a minimum light output to a maximum light output, comprising the steps of 
       generating a variable duty cycle dimming signal, the duty cycle being variable over a range of duty cycles from a minimum duty cycle corresponding to a minimum light output of the lamp to a maximum duty cycle corresponding to a maximum light output of the lamp,  
       generating a control signal representative of the duty cycle of the dimming signal,  
       generating an ac oscillator signal having a frequency determined by the control signal, and  
       generating a duty cycle of operation for the at least one controllably conductive device at the frequency of the ac oscillator signal, the duty cycle being determined by the control signal, whereby the frequency and the duty cycle of operation of the at least one controllably conductive device are independently determinable over the range of lamp light outputs from the minimum light output up to the maximum light output.  
     
     
       28. A method of selectably controlling the light output of a fluorescent lamp according to  claim 27 , wherein the step of generating the ac oscillator signal comprises varying the ac oscillator signal frequency over a range of dimming signal duty cycles corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and maintaining the frequency substantially constant over a range of dimming signal duty cycles corresponding to the intermediate light output up to the maximum light output. 
     
     
       29. A method of selectably controlling the light output of a fluorescent lamp according to  claim 27 , wherein the step of generating the ac oscillator signal comprises maintaining the ac oscillator signal frequency substantially constant over a range of dimming signal duty cycles corresponding to the minimum light output up to a light output intermediate the minimum light output and the maximum light output and varying the frequency over a range of dimming signal duty cycles above the intermediate light output. 
     
     
       30. A method of selectably controlling the light output of a fluorescent lamp according to  claim 27 , wherein the step of generating the ac oscillator signal comprises maintaining the ac oscillator signal frequency substantially constant over a range of dimming signal duty cycles corresponding to the minimum light output up to a first light output intermediate the minimum light output and the maximum light output, varying the frequency over a range of dimming signal duty cycles corresponding to the first light output up to a second light output intermediate the first light output and the maximum light output, and maintaining the frequency substantially constant over a range of dimming signal duty cycles corresponding to the second light output up to the maximum light output. 
     
     
       31. An electronic dimming ballast for gas discharge lamps, comprising: 
       a controllably conductive device adapted to supply a selected arc current to a gas discharge lamp to achieve a desired light output level from the lamp;  
       a first circuit to determine the frequency of operation of said controllably conductive device in response to a dimming signal representative of the desired light output level; and  
       a second circuit to determine the duty cycle of operation of said controllably conductive device in response to said dimming signal.